On-grid domestic battery storage

1961Nick

Martyn1981 wrote: »

I believe it's based on the possibility of discharge to the grid, not the practice.

So if you have a Tesla PWII that can maintain 5kW discharge, then theoretically, the household could discharge nearly 5kW to the grid if it wanted too from the batt, and even more if PV and batt pumping out at the same time.

If the theoretical exists, then the DNO has to consider it, in the same way that my PV permission had to be based on the whole kWp of my systems, even though E & W would never peak at the same time, in the absence of a single inverter that could cap at a lower max.

This is all true.

My system can in theory export 6.68 kWh to the grid (PV 3.68 kWh + discharge 3 kWh). Of course I would never set the battery inverter to do anything but supply power to the house, so practically it's not an issue.

I doubt the DNOs would be interested because take up of storage systems will be very low while ever the price is very high & the returns are questionable. Currently there is no motivation to export stored energy.....unless the DNO actually wants it & will pay for it.

This argument could also apply to an EV when V2H becomes more common....but on a grander scale - 90 kWh batteries with the capability of massive discharge rates!

EricMears

1961Nick wrote: »

My system can in theory export 7.68 kWh to the grid (PV 3.68 kWh + discharge 3 kWh).

3.68 kWh + 3 kWh = 7.68 kWh ?????

1961Nick

joefizz wrote: »

With the AC based system it shouldnt really be a problem though. They will all be limited to a max 16A or 13A discharge due to their nature (need to work off a household spur). Of course the chances it could go rogue are a definite possibility but with thermal runaway the issue with the DNO would be the least of your worries ;-)
The fused/tripped spur should take care of that....


As for the immersion side of things, some of us have discussed this in the past and my view is that going forward all these diverters will become redundant. They are great as standalone bits of kit but they are just a switch. Nick has mentioned a wifi switch which looks interesting and allows you to turn the immersion on and off remotely. I havent really looked into that aspect a lot as its on the long finger but having the battery power available sort of negates the need to partially divert the load to the immersion.
So instead of just sending your excess to the immersion coil, you can send a full immersion load to the coil from the solar+battery. That sort of makes the diverters obsolete and puts you fully in control. Of course the actual mechanism for putting you firmly in control has to be decided ;-)
Wait until Nick gives us an update on how he is using the wifi switch and it might be a case of sticking the diverter on ebay and buying one or more of those ;-)


All of my current plans are mostly still theoretical, they need some sun to be tested out in practice ;-)

The remote Wifi spur has been used 6 times so far & mopped up 80% of the energy that would have gone to the grid.

For it to work, you have to be fairly 'geekish' & be aware of the likely SOC of your batteries & the weather for the next 12 hours. Today....absolutely no chance of filling my batteries because there's no carry over charge & the forecast is poor. If I had a 50% charge carried over & the prospect of a sunny day, I'd be looking for a window to have a 1 or 2 hour 'burn' just after lunch.

1961Nick

EricMears wrote: »

3.68 kWh + 3 kWh = 7.68 kWh ?????

Wishful thinking or senility.....:rotfl:

Solarchaser

I can see that wifi switching is useful.
But the point is 6ou need to be watching

The idea of a diverter is fit and forget and assume it's doing the job based on solar not your geekishness as Nick says.

For ne, on good days, especially when there is carry over from previous days, the batteries can be fully charged by 9am and if the wife isn't doing her usual then I can export 30kwh in a day.

So I'd still like a diverter and thermal store.
10kwh of batteries is about right for me, it covers the base loads and most of the cooking, but cant cover the 9.6kw shower.
But solar diverter plus heat store plus thermostatic shower could, so I think it could still be very useful.

pile-o-stone

Solarchaser wrote: »

I can see that wifi switching is useful.
But the point is 6ou need to be watching

The idea of a diverter is fit and forget and assume it's doing the job based on solar not your geekishness as Nick says.

For ne, on good days, especially when there is carry over from previous days, the batteries can be fully charged by 9am and if the wife isn't doing her usual then I can export 30kwh in a day.

So I'd still like a diverter and thermal store.
10kwh of batteries is about right for me, it covers the base loads and most of the cooking, but cant cover the 9.6kw shower.
But solar diverter plus heat store plus thermostatic shower could, so I think it could still be very useful.

We have a 300l thermal store attached to two immersion heaters and have plenty of hot water for showers on a good/bright day. I do wonder whether an electric shower would be more energy efficient though in winter as we have little or no excess solar to help heat the water.

joefizz

Solarchaser wrote: »

I can see that wifi switching is useful.
But the point is 6ou need to be watching

The idea of a diverter is fit and forget and assume it's doing the job based on solar not your geekishness as Nick says.

For ne, on good days, especially when there is carry over from previous days, the batteries can be fully charged by 9am and if the wife isn't doing her usual then I can export 30kwh in a day.

So I'd still like a diverter and thermal store.
10kwh of batteries is about right for me, it covers the base loads and most of the cooking, but cant cover the 9.6kw shower.
But solar diverter plus heat store plus thermostatic shower could, so I think it could still be very useful.

I dont disagree, but it is very passive at the mo and it does depend on your usage and thats the over-riding thing for all of us, our usage.
Theres probably no getting round your shower if you consider just using everything as is.

For myself its a case of putting the immersion on for 15 mins before a shower to get enough hot water for a showers worth, thats my system though and it wont work for everyone.

I dont have showers at the same time each day or indeed only have one per day (or none ;-)) so manual intervention is ideal for me, rather than have a complete (or partially complete) tank of hot water on the go just in case.
Im similar to you with the battery, have the 9.6kwh setup and its enough, its probably more than enough but allows me to run everything off the battery (hence thermostatic mixer shower with immersion setup), im still early stages (in my terms) with monitoring it all and would like a full years worth of data now Ive stopped tinkering with the main infrastructure!



With pile-o-stones point about the electric shower, again it depends on usage, like my previous comments with the battery, installing the battery allowed me to think differently and apply the same stuff in different ways, to harness the inner geek as it were ;-)



Im in the same boat as Nick as its unlikely the next couple of days will allow a lot of scope for experimentation so having been through all this and planning an automated system, one of the feeds into that system I will look at will be next days weather forecast! All the measuring tools I have already have todays weather built in so even just a rough idea of the next 24hrs will be ideal.
I already do this manually (planning to use about 16kwh additional daytime on Sat - or next sunny day) and put washing machine/dishwasher on certain times.

Ive been limiting ASHP to an hour or two per evening this last week, bumping temp up and using it to generate a lot of hot air to put around the house... not quite what the designers had in mind but still... .. using it not to maintain a constant temperature but a minimum one. I guess I was used to lighting the fire and then letting it die out overnight...
At the minute Im just gathering the data on this, it might be better to just let the ashp run but its just been too cold here recently (or Ive just felt the cold more) to not have the oil heating on at some point during the night. We had warnings of ground frost last week!


It will be interesting to get everyones thoughts/experiences during mid december as thats the stress point for all of us. I had originally planned to move 2 panels from E/W to a steep south facing angle primarily for this time but now Im not so sure. I still havent maxed out my inverter yet this year although was coming close at the end of may, since then Ive been lucky to refill the battery ;-) So unless we get a typically sunny week coming up to midsummer then I'll have to wait to next year for that data.

Solarchaser

Yeah I agree, its entirely about usage.

Something like an ashp is useless to me, as the wife enjoys opening a window in every room every day.... and then putting the central heating on:eek:

You are in the lucky position of living alone and so can dictate what will happen day to day and prioritise using most of the leccy on a bright day.

I can plan... but the wife does what the wife does.
It's not unusual for her to put a load in the washing machine, another in the tumble dryer, start the dishwasher and then go for a shower.:o

I'm also away fairly often with work, so I need the system to be as automated as possible.

I'm toying with the idea of the thermal store with motorised valves to isolate it with minimum temperature, but when temperature is high enough, to stop the combi boiler for hit water, this way the winter is exactly the same as now, but I'd assume my summer hot water needs would be covered.

I just need to work out how to do it.... cheaply

Reed_Richards

Solarchaser wrote: »

I'm toying with the idea of the thermal store with motorised valves to isolate it with minimum temperature, but when temperature is high enough, to stop the combi boiler for hit water, this way the winter is exactly the same as now, but I'd assume my summer hot water needs would be covered.

I have been thinking along similar lines. One option I have not resolved is whether I should try to heat the water in the tank to tepid in winter and then (plumbing permitting|) use this as the in-feed to my Combi boiler so it does not have to heat the water so much.

Solarchaser

Yeah I like that idea Reed, as it would reduce energy usage, and even if the cylinder was unheated in winter, getting the 4c water to run through it before boiler would at least bring it up another 10c or so assuming the thermal stole would be sitting at room temperature.

However I've done a fair bit of reading about this on boiler forums, and most gas engineers advise against putting hot water through the boiler, so for me the problem would be the switch over point.

If it's too cold to be hot water, but too warm to go through the boiler...

I still like the idea, but I cant do it atm as boiler is downstairs as is incoming water, and only place for thermal store is 2 floors up, in loft.
The wife wont let me tear into the kitchen to run more pipes as it was just redone a wee while ago.